This invention relates to a thick-film integrated circuit device, and more particularly, to a thick-film integrated circuit device which has a resistance-trimming resistor and a function-trimming resistor, and can be manufactured by means of an easy-to-perform trimming opera ion.
Most thick-film hybrid IC (integrated circuit) devices have an insulating substrate on which resistors are formed by means of a thick-film forming method consisting the steps of forming layers of resistive paste on the substrate and firing these resistive paste layers. Electronic components are mounted on the insulating substrate. The resistance which the device has after the electronic components have been provided on the substrate is different from the desired value by 10 to 25%, due to the difficulties of preparing a paste of the desired composition, and forming and firing the paste layers under appropriate conditions.
To correct the resistance of the thick-film hybrid IC device, technique called "trimming" is performed. More specifically, a resistance-trimming resistor and a function-trimming resistor are formed on the insulating substrate, by means of thick-film method. Then, a laser beam is applied to resistance-trimming resistor, thereby removing a portion of the resistor. This process is called "resistance trimming." Thereafter, a laser beam is applied to the function-trimming resistor, thus removing a portion of the function-trimming resistor. This process is called "function trimming." The resistance trimming and the function trimming, thus performed, impart the desired resistance to the thick-film hybrid IC device.
A thick-film hybrid IC device of the type described above comprises an insulating substrate, three conductors, a resistance-trimming resistor, and a function-trimming resistor. The conductors are rectangular strips formed on the insulating substrate and arranged in a line, spaced apart from one another. The three conductors and the two trimming resistors are made by means of the thick-film forming method. The first conductor has a pad portion at one end, and a connecting portion at the other end. The second conductor, which is located between the first and third conductors, has two connecting portions at the ends, respectively. The third conductor has a pad portion at one end, and a connecting portion at the other end. The resistance-trimming resistor, which is a rectangular strip, is formed on the substrate, with two ends overlapping the connecting portion of the first conductor and one connecting portion of the second conductor, respectively. The function-trimming resistor, which is also a rectangular strip, is formed on the substrate, with two ends overlapping the other connecting portion of the second conductor and the connecting portion of the third conductor, respectively. Hence, the resistance-trimming resistor is electrically connected to the first and second conductors, and the function-trimming resistor is electrically coupled to the second and third conductors.
As has been mentioned, the resistance of the thick-film hybrid IC devices is corrected by means of trimming. The trimming is carried out, while the resistance between the pad portions of the first and third conductors is being measured. First, a laser beam is applied to the resistance-trimming resistor, thus cutting a notch in this resistor. Next, electronic components, including capacitors, are mounted on the insulating substrate. Finally, a laser beam is applied to the function-trimming resistor, thereby cutting a notch in the function-trimming resistor, while the time constant of the circuit composed of the electronic components is being measured. The resistance of the thick-film hybrid IC device is thus determined by the two trimming operations.
Before a notch is cut in the resistance-trimming resistor, the thick-film hybrid IC device has a resistance different from the desired value by 10 to 25%. It is extremely difficult to trim resistance-trimming resistor to such extent that this resistance difference is completely eliminated. A considerable resistance difference still remains even after the resistance-trimming resistor has been trimmed and the electronic components have been mounted on the insulating substrate. Hence, in some cases, a relatively long notch must be cut in the function-trimming resistor, in order that the device may have a resistance substantially equal to the desired value. When the notch cut in the function-trimming resistor is too long, however, the resistor has too narrow a current path, with the result that an abnormally high level of heat will be generated therein.